1. Field of the Invention
The present invention relates to an apparatus and process for expanding a tube. More particularly the apparatus and process of the present invention comprise the compression and resultant selective radial expansion of elastomeric bars against the inner surface of the tube to radially expand the walls of the tube at the locations of contact with the expanded elastomeric bars. The utility of the invention lies in its low cost tooling for complex tubular forming operations. The use of elastomeric bars allows tubular forming into a variety of shapes including elliptical, splined round, or corrugated round.
2. Description of the Prior Art
There are many methods of expanding the radius of a tube by a force located internally to the tube. Prior art methods of expanding tubes use metal rollers that move outwardly from a central position within the tube as the metal rollers are mechanically rotated about the central position. Metal rollers however can expand only to a round shape and they are limited to force applications near the free end of the tube. Other methods involve the compression and resultant expansion of high pressure fluid against the inner walls of the tube to radially expand the tube walls. Disadvantages with this method include complicated tooling involving complexly shaped seals which are prone to leakage. Other prior art such as U.S. Pat. No. 4,109,365 by Tygart involve the compression of a hard rubber or elastomer by piston forces applied from both ends of the tube, instead of one end as taught in my invention, thereby making it difficult to expand the tube at a great distance from either end of the tube.
U.S. Pat. No. 4,006,619 by Anderson discloses a tube expander utilizing hydraulically actuated pistons which compress a resilient element to radially expand a tube completely about its circumference. My invention teaches the selective expansion of a tube wall at intermittent locations about the circumference of a tube by compression and resultant expansion of elastomeric bars against the inner surface of the tube. Selective expansion may be used to form corrugated or splined tubular ends which may be useful in heat exchanger tubes to increase gas turbulence and heat transfer. Therefore, what is needed and what has been invented is an apparatus and process for selectively expanding a tube, without the foregoing deficiencies associated with prior art apparatuses.